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Monday, 26 October 2009

What might the ice stream have carried?



Stones from the Brecon Beacons?

Thanks again, Ed. This is all very intriguing -- I really want the geomorphologists and glaciologists in on this. We do actually have a pretty mottley collection of stone types or provenances at Stonehenge -- 27 or so at the last count? Some of them are Preseli igneous rocks, but others aren't. There are some fragments still unidentified. And the Altar Stone is a pretty large erratic, identified by Kellaway a long time ago as coming from the Senni Beds in the Brecon Beacons -- and now that identification has been confirmed by other geologists too. So that must be one "South Wales" erratic carried southwards by Welsh ice and then eastwards by Irish Sea ice. Did all of this happen in one glacial episode, or two, or three? Still great problems and mysteries! I have touched on these in my book.

The best glacial deposits are at Court Hill, at the western edge of the Mendips -- tills 24m thick. I need to check out what the erratic assemblage is.

How tight were the bends in the ice movements? It's all speculation at the moment. As you might have observed, I have played about with a few variations on the theme, and am still none the wiser.....

1 comment:

Anonymous said...

Brian, odd how you should mention the Altar Stone, I was just coming to it, but this bothers me - not so much that it keeps me awake at night, but it is pretty unique. This stone seems to have been erected on the mid summer sunrise axis at Stonehenge and being of micaceous sandstone must have been an impressive sight when highly polished with the sun hitting it.

But (and this is what bothers me), why only one - do you know of any others deposited along the glacial trail?

Best wishes,
Ed Watson